When certain avionics equipment break down or certain operational capacities fail, the anomaly or anomalies are detected by avionics systems responsible for monitoring them. These equipment breakdowns or operational capacity failures are communicated to the pilot using an alert system, such as a Crew Alerting System (CAS) or a Flight Warning System (FWS), depending on the aircraft builders.
The pilot must next interpret the breakdown or failure messages presented by the alert system, such as the FWS, and the various instruments of the dashboard.
The pilot must then first perceive the received information, then understand it by using his memory, and lastly react by using his experience.
The understanding of the situation is based on the recognition of the signature of the breakdowns or failures that he may have recorded during his training or experience. “Signature of a failure” refers to all of the observable effects of an operational capacity failure or avionics equipment breakdown.
This signature recognition mechanism is effective when the failures are simple and their effects are easily recognizable and unambiguous. The effects of a failure are ambiguous when several failures have the same effects.
However, once several breakdowns and/or failures are present at the same time, whether independently of one another or caused by one another, then the signatures of these breakdowns and/or failures become superimposed, such that it is very difficult for a pilot always to adopt an appropriate reaction.